The present invention relates to an airbag apparatus mounted on a passenger seat of a motor vehicle, or the like. More particularly, the present invention relates to an airbag apparatus in which a door opens while being lifted into a vehicle cabin when the airbag is expanded. The present invention further relates to a cover for use in the airbag apparatus.
An airbag apparatus for a passenger seat mounted on a motor vehicle is provided with a folded airbag, a retainer to which the airbag is attached, an inflator (a gas generator) for expanding the airbag, a module cover or a module cover door portion to be disposed in front of the retainer, and the like.
When the inflator generates the gas, the airbag starts expanding operation, and the module cover or the module cover door portion is pushed open along a tear line so as to burst open. The airbag is then developed in a vehicle cabin to protect an occupant.
An airbag apparatus is disclosed in Japanese Unexamined Patent Application Publication No. 2003-137054, in which an airbag is configured such that, when the airbag is expanded, a door portion of a module cover is opened while being lifted toward a vehicle cabin so that the door portion of the module cover is smoothly opened.
FIG. 4 is a cross-sectional view illustrating the airbag apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2003-137054. FIG. 5 is a cross-sectional view illustrating the airbag apparatus in operation. FIG. 6 is a perspective view illustrating a door frame of the airbag apparatus.
As illustrated in FIG. 4, an airbag 52 being folded, (in FIG. 5) is housed in a retainer 50, which has a shape of an open-top container and is configured to be capable of being expanded by an inflator 54.
A portion above the retainer 50 is covered with a module cover (instrument panel) 60. Concave ridge-shaped tear lines 62a, 62b are formed in a module cover 60. A tear line 62b is formed to extend around along an upper edge of the retainer 50, and an inside area surrounded by the tear line 62b serves as a door portion 64. The tear line 62a extends so as to longitudinally traverse through a center of the door portion 64.
A door frame 70 formed of a door frame movable member 72 and a door frame fixed member 74 is provided at a rear face of the module cover 60. The door frame fixed member 74 has a rectangular frame shape and the door frame movable member 72 is slidably fit into inside thereof.
The door frame movable member 72 is provided with a lining plate portion 72a overlapping with the door portion 64 of the module cover 60 and a leg piece 72b that serves as a leg portion extending downward from both sides of the lining plate portion 72a as shown in FIG. 4, and a hooking hole 72c is formed in the leg piece 72b. A tear line 72d is formed in the lining plate portion 72a in a position overlapping with the tear line 62a. A hinge groove 72e formed of a concave ridge is provided along an intersecting corner portion of the lining plate portion 72a with the leg piece 72b. 
The lining plate portion 72a is fixed to a rear face of the door portion 64 of the module cover 60 by means of vibration welding.
The door frame fixed member 74 is provided with a leg frame 74a serving as a rectangular frame-shaped leg portion extending around an outer periphery of the retainer 50, and a flange portion 74b extending outward from an upper end of the leg frame 74a. The flange portion 74b is fixed to a peripheral portion of the door portion 64 in the module cover 60 by means of vibration welding. A hooking hole 74c is formed in the leg frame 74a. 
A hook 78 fixed to the retainer 50 is inserted into the hooking holes 72c, 74c. 
When the inflator 54 is operated to discharge gas, the door frame movable member 72 is moved upward (lifted) by being pressed upward by the expanding airbag 52, as shown in FIG. 5. The module cover 60 is burst along the tear line 62b and the door portion 64 is cut off from the surrounding module cover 60. The door portion 64 is further moved upward with the door frame movable member 72, and the tear line 72d of the lining plate portion 72a and the tear line 62a of the door portion 64 are burst by being pressed by the airbag 52. Further, the door portion 64 starts to open like a door being separated into two ways of the left and the right direction and the airbag 52 is expanded in a vehicle cabin as shown in FIG. 5.
Thus, the door portion 64 performs lifting operation and is separated from the surrounding module cover 60, and thereby, the door portion 64 smoothly starts to open without receiving reaction force against a deformation from the surrounding module cover 60.
In an airbag apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2003-137054, illustrated in FIGS. 4 through 6, a door frame fixed member 74 and a door frame movable member 72 are respectively molded into bodies separated from a module cover 60 and are combined with the module cover 60 by means of an ultrasonic welding process (described in the aforementioned reference in paragraph number 0016).
Thus, when module cover 60, the door frame movable member 72, and the door frame fixed member 74 are separately molded, and are fixed by means of the ultrasonic welding, a large amount of effort is required to conduct the molding and welding work. Further, the desired degree of positioning accuracy may not be obtained in the door frame movable member 72 and the door frame fixed member 74.
It is therefore an object of the present invention to facilitate the manufacture of a cover of an airbag apparatus, and to improve the dimensional accuracy of the cover in which a door frame movable member and a door frame fixed member are provided at a rear face of an interior panel, and in which a door portion is opened while the door frame movable member is being lifted.
Further objects and advantages of the invention will be apparent from the following description of the invention and the associated drawings.